Material expression custom - relative Include File Path?

Hello,

I was hoping I could use a relative file path pointing to a file inside the content folder, however using /Game/Shaders/myHeader.ush I get the error “Can’t map virtual shader source path …”
"Directoy mappings are :
/Engine, /Plugin…
"

Is there a way to add to this list or somehow have a relative path?

Thanks a lot

*I had the same problem